In the act of exchange, as in the transmission of power by machinery, there is friction to be overcome, losses which must be borne, and limits which … - Antoine Augustin Cournot

Those skilled in mathematical analysis know that its object is not simply to calculate numbers, but that it is also employed to find the relations between magnitudes which cannot be expressed in numbers and between functions whose law is not capable of algebraic expression.

Anyone who understands algebraic notation, reads at a glance in an equation results reached arithmetically only with great labour and pains.

The employment of mathematical symbols is perfectly natural when the relations between magnitudes are under discussion; and even if they are not rigorously necessary, it would hardly be reasonable to reject them, because they are not equally familiar to all readers and because they have sometimes been wrongly used, if they are able to facilitate the exposition of problems, to render it more concise, to open the way to more extended developments, and to avoid the digressions of vague argumentation.